Need help with ecm/transmission
 

I have a 2005 cummins. It is throwing 3 codes for gov pressure/transducer, throttle acuator and transmission circuit relay. It says low power voltage on each code. I have replaced each and still get the codes. Sometimes they go away but when they dont the truck starts off in 3rd gear and wont shift into overdrive. Its been at 2 different transmission shops and they checked over everything and didnt find anything. I was told by a diesel shop a few months earlier that my ecm was going out and was told by a mechanic today that it sounded like my ecm. I found a ecm at a decent price. Should i try it? or maybe the pcm? Thanks guys

No one?